The existence and use polycrystalline diamond material types for forming tooling, cutting and/or wear elements is well known in the art. For example, polycrystalline diamond (PCD) is known to be used as cutting elements to remove metals, rock, plastic and a variety of composite materials. Such known polycrystalline diamond materials have a microstructure characterized by a polycrystalline diamond matrix first phase, that generally occupies the highest volume percent in the microstructure and that has the greatest hardness, and a plurality of second phases, that are generally filled with a solvent catalyst material used to facilitate the bonding together of diamond grains or crystals together to form the polycrystalline matrix first phase during sintering.
PCD known in the art is formed by combining diamond grains (that will form the polycrystalline matrix first phase) with a suitable solvent catalyst material (that will form the second phase) to form a mixture. The solvent catalyst material can be provided in the form of powder and mixed with the diamond grains or can be infiltrated into the diamond grains during high pressure/high temperature (HPHT) sintering. The diamond grains and solvent catalyst material is sintered at extremely high pressure/high temperature process conditions, during which time the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure.
Solvent catalyst materials used for forming conventional PCD include solvent metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from about 85 to 95% by volume diamond and a remaining amount being the solvent metal catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstices or interstitial regions that exist between the bonded together diamond grains and/or along the surfaces of the diamond crystals.
The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired. Industries that utilize such PCD materials for cutting, e.g., in the form of a cutting element, include automotive, oil and gas, aerospace, nuclear and transportation to mention only a few.
For use in the oil production industry, such PCD cutting elements are provided in the form of specially designed cutting elements such as shear cutters that are configured for attachment with a subterranean drilling device, e.g., a shear or drag bit. Thus, such PCD shear cutters are used as the cutting elements in shear bits that drill holes in the earth for oil and gas exploration. Such shear cutters generally comprise a PCD body that is joined to substrate, e.g., a substrate that is formed from cemented tungsten carbide. The shear cutter is manufactured using an HPHT process that generally utilizes cobalt as a catalytic second phase material that facilitates liquid-phase sintering between diamond particles to form a single interconnected polycrystalline matrix of diamond with cobalt dispersed throughout the matrix.
The shear cutter is attached to the shear bit via the substrate, usually by a braze material, leaving the PCD body exposed as a cutting element to shear rock as the shear bit rotates. High forces are generated at the PCD/rock interface to shear the rock away. In addition, high temperatures are generated at this cutting interface, which shorten the cutting life of the PCD cutting edge. High temperatures incurred during operation cause the cobalt in the diamond matrix to thermally expand and even change phase (from BCC to FCC), which thermal expansion is known to cause the diamond crystalline bonds within the microstructure to be broken at or near the cutting edge, thereby also operating to reduces the life of the PCD cutter. Also, in high temperature oxidizing cutting environments, the cobalt in the PCD matrix will facilitate the conversion of diamond back to graphite, which is also known to radically decrease the performance life of the cutting element.
Attempts in the art to address the above-noted limitations have largely focused on the solvent catalyst material's degradation of the PCD construction by catalytic operation, and removing the catalyst material therefrom for the purpose of enhancing the service life of PCD cutting elements. For example, it is known to treat the PCD body to remove the solvent catalyst material therefrom, which treatment has been shown to produce a resulting diamond body having enhanced cutting performance. One known way of doing this involves at least a two-stage technique of first forming a conventional sintered PCD body, by combining diamond grains and a solvent catalyst material and subjecting the same to HPHT process as described above, and then removing the solvent catalyst material therefrom, e.g., by acid leaching process.
Known approaches include removing substantially all of the solvent catalyst material from the PCD body so that the remaining PCD body comprises essential a matrix of diamond bonded crystals with no other material occupying the interstitial regions between the diamond crystals. While the so-formed PCD body may display improved thermal properties, it now lacks toughness that may make it unsuited for particular high-impact cutting and/or wear applications. Additionally, it is difficult to attach such so-formed PCD bodies to substrates to form a PCD compact. The construction of a compact having such a substrate is desired because it enables attachment of the PCD cutter to a cutting and/or wear device by conventional technique, such as welding, brazing or the like. Without a substrate, the so-formed PCD body must be attached to the cutting and/or wear device by interference fit, which is not practical and does not provide a strong attachment to promote a long service life.
It is, therefore, desirable that a polycrystalline diamond construction be engineered in a manner that not only has improved thermal characteristics to provide an improved degree of thermal stability when compared to conventional PCD, but that does so in a manner that avoids unwanted deterioration of the PCD body that is known to occur by the presence of the solvent catalyst material initially used to form the PCD construction at or near the working surface. It is further desired that such polycrystalline diamond constructions be engineered in a manner that enables the attachment of a substrate thereto, thereby forming a thermally stable polycrystalline diamond compact that facilitates attachment of the polycrystalline diamond compact to cutting and/or wear devices by conventional method, such as by welding, brazing, or the like.